A related heating apparatuses and heating coils are configured to heat an annular workpiece. For example, it is described in Patent Document 1 identified below that, in order to heat an annular workpiece by induction heating, a zigzag heating coil is opposed to a portion of the annular workpiece, and the annular workpiece and the heating coil are moved relative to each other, for example by rotating the annular workpiece so that a treatment target portion in a form of an endless loop is induction-heated.